Turbochargers are used in vehicle engines to increase the power output of the engine without increasing the size of the engine, specifically, the cylinder displacement. That is, a turbocharger can significantly improve the power-to-weight ratio for the engine. A turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute. Power increases of 30 to 40 percent are typical for turbocharged engines.
Unfortunately, turbochargers do not provide an immediate power boost during a launch event. A time period, typically measured in seconds or fractions of seconds is needed for the turbine to reach the speeds necessary to produce the desired boost. This phenomenon, known as “turbo-lag,” results in a hesitation at the start of a launch event. It is known to decrease turbo-lag by reducing the inertia of the rotating parts in the turbocharger, mainly by reducing the weight of the parts. This weight reduction enables the turbine and compressor to accelerate more quickly, and start providing boost earlier. Inertia can be reduced by reducing the size of the turbocharger. Unfortunately, a smaller turbocharger may not be able to provide adequate boost at higher engine speeds. Also, a smaller turbocharger may rotate at excessive speeds.
For turbocharged engines in vehicles with torque converters, it is known to use a “loose” torque converter. This arrangement allows the engine to attain higher speeds during the launch event, decreasing the time necessary for the turbocharger to reach the desired speed. Unfortunately, this configuration results in a decrease in fuel economy across the entire operating range of the torque converter.
Thus, there is a long-felt need for a means to reduce turbo-lag without compromising fuel economy or the performance of the turbocharger.